# Learning Ruby with AtCoder 6 [Contest 168 Therefore]

## Introduction

As part of learning Ruby, we will challenge "competitive programming (competitive professional)". We will output what we have learned in the learning for that purpose. This time from the first question (Therefore) of "At Coder Beginners Contest 168". https://atcoder.jp/contests/abc168/tasks/abc168_a

I will summarize it based on the solution I used and the commentary published from the official.

## problem

When counting pencils in Japanese, "book" is added as a classifier after the number. How to read this classifier differs depending on what number it is attached to. For integers less than or equal to 999, how to read "book" when saying "N books" is

・ When the 1st place of N is "2,4,5,7,9",'hon' ・ When the 1st place of N is "0,1,6,8",'pon' ・ When the 1st place of N is "3", it is'bon'

Given N, print out the corresponding "book" reading.

Constraint N is a positive integer less than or equal to 999

The input is given in the following form.

``````N

#Example
16
``````

In the above example, it can be divided up to 2 times.

``````Output example
#In the case of the above example
=> pon
``````

First is the code I wrote first.

``````a = gets.to_i.modulo(10)
if [2,4,5,7,9].include?(a)
print "hon"
elsif [0,1,6,8].include?(a)
print "pon"
else
print "bon"
end
``````

Use the modulo method to receive only the ones digit from the input Judgment is made by the if statement and the include? Method. include? As for the method, I wrote about the following article once, so [Ruby learning [Some Sums] with AtCoder Beginners Selection](https://qiita.com/jag_507/items/cd3ad74d77ad933897b7#include%E3%83%A1%E3%82%BD%E3%83%83 % E3% 83% 89range% E3% 82% AF% E3% 83% A9% E3% 82% B9) Here, I will touch on the modulo method.

### modulo method

Returns the remainder divided by the specified number. In the answer, the ones digit is taken out as a remainder by dividing the integer by 10.

``````#Example
13.modulo(4)
=> 1
42.modulo(10)
=> 2
``````

In the commentary distributed after the contest, A more intuitive way to write with a case statement is introduced.

In the following, we will introduce the case statement after answering with the case statement.

``````n = gets.to_i.modulo(10)
case n
when 2,4,5,7,9
print 'hon'
when 0,1,6,8
print 'pon'
else
print 'bon'
end
``````

In the first answer, I put the condition in an array and made a judgment with the include? Method, By using the case statement, you can write the code as if you were thinking "If the first place is 2,4,5,7,9 ...". Certainly this one seems to be better.

### case statement

This is useful when searching for a match from multiple candidates for a single value. The "===" operator determines whether it matches what is specified by when.

``````case object
when value1
# object ===Statement to be executed when value1
when value2
# object ===Statement to be executed when value2
else
#Statement to execute if all are not matched
end
``````

The "===" operator that appears here is If the object mentioned above is a character string or a numerical value, set it as "==". For regular expressions, use "= ~" In the case of a range, it seems to judge whether the value is included in it like include? It seems to be flexible and easy to use.

## Finally

So far, we have introduced the methods learned from the first question (Therefore) of "AtCoder Beginners Contest 168".

If you have any mistakes, I would be grateful if you could point them out.